Groundbreaking solutions for remediation using bacteria
Bacteria lower costs and are reliable – when they are cleaning up contaminated land, at least. But which bioremediation technologies are the best on the commercial scale? Biotechnology organisation BIO-WISE and construction industry body the Construction Industry Research and Information Association (CIRIA) have been working together for 18 months on a project that demonstrates the best of the best.Given the right conditions, bacteria literally eat pollutants in contaminated ground, breaking down oils, solvents and fuels into nothing more harmful than carbon dioxide and water. What is more, they tend to get the job done more cheaply, more reliably and potentially with far less disruption than conventional methods. They can also be used as the detection system for novel biosensors to assess the toxicity of contaminants in soil and groundwater.
A good idea of the range of applications in current use in the UK is contained in a new leaflet, Biological Methods For Contaminated Land Management, which was supported by BIO-WISE and summarises a selection of case studies contained in CIRIA publication C575.
The first stage of the windrows project involves excavating the site
For example, one case study looks at how windrows, a form of composting, were used to clean up an urban riverside site spoilt by total petroleum hydrocarbons (TPH), polynuclear aromatic hydrocarbons (PAHs), benzene, toluene, ethylbenzene and xylenes (BTEX) and PCBs.
The contaminated soils were excavated, screened for large bits of concrete and rubble and then laid out on a concrete hardstanding in a series of windrows covered with tarpaulins. The rows were mixed with composts and turned regularly. Within seven weeks most of the soil was clean enough to be re-used on the site. Excessive lorry movements were avoided and some £1.8 million was saved in comparison to excavation and landfill.
The second case study covers monitored natural attenuation (MNA), a harnessing of natural processes that takes place in the ground to limit the spread of contamination. In this instance, the problem was nitrobenzene that had leaked from a bulk storage plant and extended in a plume to a river alongside the site. Monitoring of the ground and surface water established that natural processes could be relied on to protect the river quality. Of the remediation options available, MNA was the most cost-effective and had least impact on manufacturing activities.
In the third case study, ‘biosparging’ was used to treat a former gasworks where groundwater was contaminated by benzene, toluene, ethylene and xylene (BTEX), phenols and polyaromatic hydrocarbons (PAHs) in a sand aquifer beneath the site. The solution involved the circulation of air through a series of injection wells to increase oxygen levels and stimulate biodegradation by aerobic bacteria. The sparging system resulted in significant savings over alternative options, required little maintenance and caused minimal impact.
A final example is of a biological method used to test soil quality in an area where air emissions from smelting had caused a build-up of metal contaminants including cadmium, copper, lead and zinc in the ground. Biological testing using biosensors is inexpensive, produces results within 24 hours and can detect toxicity that chemical analysis might miss.
All the examples described in the leaflet involve tried-and-tested techniques and technologies that have significant advantages over more expensive and cumbersome forms of contaminated land management. They are among a range of biological solutions that are coming into their own as economic, social and legal pressures grow to minimise pollution and restore prime brownfield sites.
For more information and a free copy of the above leaflet or a technical review on contaminated land remediation contact BIO-WISE, the Government programme dedicated to helping UK industry benefit financially and environmentally from biotechnology. Helpline: 0800 432100. Email: firstname.lastname@example.org. To obtain a copy of CIRIA publication C575, please contact CIRIA on 020 7222 8891.